Modern printers use a variety of inks to generate images from data. These inks may include liquid ink, dry ink, also known as toner, and solid ink. In liquid ink jet printers, the liquid ink is typically stored in cartridges, which are installed in the printers, and delivered to a print head. Solid ink printers, however, are loaded with blocks or pellets of solid ink that are transported to a melting device where the solid ink is heated to a melting temperature. The melted ink is collected and delivered to a printhead.
In both liquid ink and solid ink printers, the liquid ink is provided to a printhead and selectively ejected onto media, such as paper, advancing past the printhead, or onto a rotating offset member. In offset printing machines, the image generated on the rotating offset member is transferred to media by synchronizing passage of media and rotation of the image on the member into a transfer nip formed between a transfix roller and the offset member. The printheads for liquid ink and solid ink printers typically include a plurality of ink jet stacks that are arranged in a matrix within the printhead. Each ink jet stack has a nozzle from which ink is ejected by applying an electrical driving signal to an actuator in the ink jet stack to generate a pressure pulse that expels ink from a reservoir in the ink jet stack.
A partially assembled ink jet stack is shown in a cross-sectional side view in FIG. 4. The ink jet stack 10 includes a nozzle plate 14, an inlet plate 18, a body plate 22, and a diaphragm plate 26. These plates are assembled and bonded to one another using adhesives in a known manner to form ink jet stack 10. The nozzle plate 10 includes a plurality of openings 30, which act as nozzles for ink expelled from ink supplies 34. Ink enters the ink supplies 34 through inlets 38. The diaphragm plate 26 is made of a resilient, flexible material, such as stainless steel, so the plate can move back and forth to expel ink in one direction of movement and to induce movement of ink into the supplies 34 in the other direction of movement. Movement is actuated by the reaction of the actuator 42, to the input of electrical energy provided through conductive adhesive 46 and an electrical contact pad 50. The electrical contact pad 50 is mounted to a support member 54, such as a flex cable or an electrical circuit board (ECB), which is partially supported by standoffs 58, which are also mounted to the support member 54. The actuator may be a piezoelectric material, such as lead-zirconium-titanate, which is sandwiched between two electrodes. An electrical signal generated by a printhead controller is conducted by an electrical lead to the electrical contact pad 50 and then through the conductive adhesive to the electrode contacting the adhesive. The charge on the electrode results in an electric field between the two electrodes on opposite sides of the actuator material. The direction and strength of this electric field induces the piezoelectric material to deflect in one direction or another to either expel ink from the ink supply or to induce ink to enter the ink supply through the ink inlet.
The actuators 42 are arranged in an array on a substrate 400 as shown in FIG. 5. Horizontal channels 408 and vertical channels 410 are cut into the substrate 400 to isolate the actuators 42 from one another mechanically. Adhesive is applied to the diaphragm layer 26 at positions that corresponds to locations the actuators touch after the two substrates are mounted together. The diaphragm layer 26 and the actuator substrate 400 are pressed into contact with one another to bind the two layers together. This assembly enables the deflection of the actuators to move the diaphragm layer, which is immediately adjacent to the ink supply area.
In some ink jet heads, each row of actuators is coupled to ink supply areas having a different color of ink. A phenomena known as secondary banding has been observed in these printheads. Secondary banding occurs when mechanical jitter causes the ejected ink to land at non-uniform intervals on the imaging material. As a consequence, the printing of secondary colors, which requires two colors of ink to be printed on top of one another, may produce inconsistent results. A uniformly generated secondary color is shown in FIG. 6, while secondary banding is shown in FIG. 7. Attenuation of the inconsistent ejection of the ink that produces secondary banding is desirable.